Straphangers had to endure another round of nightmare delays on the line Tuesday — the second straight day of mishaps since the MTA introduced new signal technology that is supposed to make the service more reliable.

Trouble on the line Tuesday began around 5:45 a.m., when one train’s emergency brakes were “automatically activated” at the Vernon Boulevard-Jackson Avenue station in Queens, the MTA tweeted.

The snafu caused No. 7 trains to run with delays in both directions.

Roughly an hour later, the line’s 34th Street-bound express train service was knocked out while transit crews removed a train from service near Queensboro Plaza.

“Expect delays in both directions until congestion clears,” the MTA tweeted.

The train issues caused headaches for commuters.

Serge Kovaleski, a reporter for the New York Times, said in a tweet that after a 20-minute wait at the Vernon Boulevard-Jackson Avenue station, a No. 7 train arrived at the platform “jammed with commuters,” and “it keeps going without stopping.”

“The @MTA is incapable of providing basic service to New Yorkers,” Kovaleski tweeted.

Another commuter, Maggie O’Rourke, tweeted: “@MTA 7 train delays the last 2 days. Last night’s ride home was horrendous over 2 hours to get home. This morning more problems.”

Jennie McCarthy wrote, “@MTA another morning of delays on the 7 train. Could you plan for these so we could get [to] work on time for once? Really frustrating – it’s the norm to have morning delays.”

On Monday, there was chaos on the line because of a communication problem at the Queensboro Plaza station, which jammed up the evening commute.

Earlier Monday, the MTA had trumpeted that “modern signaling is live on the entire 7 line.

“After we finish optimizing and automating the system and performing other signal work over the coming weeks, we’ll be able to run more trains, more reliably. Thank you for your patience,” the transit authority tweeted.

The line’s Vernon Boulevard-Jackson Avenue station will be one of the main sites servicing Amazon’s planned massive headquarters in Long Island City.